1. Field of the Invention
The present invention relates to, for example, a rotor of a synchronous induction motor which starts using induction torque and performs synchronous operation using reluctance torque and devices employing the rotor.
2. Description of the Related Art
FIGS. 11 through 13 show a conventional synchronous motor (4 poles): FIG. 11 shows a cross section viewed from an output axis of the synchronous motor; FIG. 12 shows a cross section viewed from a side of the output axis of the synchronous motor; and FIG. 13 shows a cross section of a rotor of the synchronous motor. In the figures, a reference numeral 1 shows a rotor which is fixed to an output axis 3 by such as press fit and formed by laminating in an axial direction. A reference numeral 12 shows a slit which is provided in parallel with another slit in the radial direction so as to become projected toward the center, which is magnetically insulated so as to magnetically induce from a magnetic pole at the rotor 1 to a next magnetic pole.
A reference numeral 9 shows a stator formed by laminating electromagnetic steel plates in the axial direction. 10 shows a coil wound around the stator 9, and a rotation magnetic field is generated by inducing electric current to the coil 10. A part B in FIG. 13 shows a thin connection part, which is a part of a periphery of the rotor 1 and is partially connected to another connection part so as not to separate by slits 12, and which holds the strength of the rotor. The partial connection of the thin connection part can be provided at each part of the rotor 1 to support the strength of the rotor within a range not to disturb the magnetic properties of the motor.
In the synchronous motor formed as described above, it is possible to generate rotation power of the rotor 1 by running exciting current to the coil 10 of the stator 9 so that magnetomotive force acts in direction of the magnetic pole of the magnetic field of the rotor 1. In case of the motor shown in FIG. 11, the rotor rotates following (synchronizing) the rotation magnetic field which is generated by the coil 10 of the stator 9 due to the reluctance torque.
When the rotational position of the rotor 1 is detected using such as a rotational position detector, the magnetic field flux and the torque current can be controlled arbitrarily and precisely, so that it can be said that the synchronous motor is good in controllability as well as a permanent magnet synchronous motor which is highly effective. Further, compared with the induction motor which is generally used, the synchronous motor shown in FIG. 11 does not need secondary electric current running to the rotor, and loss of the rotor is small since there is no rotor copper loss, which makes the motor highly effective.
The conventional synchronous motor is formed as described above, so that there are following problems.
In the rotor 1 of the synchronous motor shown in FIG. 11, the slit 2 is provided to achieve the above performance so as to generate reluctance torque. Accordingly, to keep the form of the rotor, the thin connection part is provided at both ends of the slit 12, fixed mechanically, and the strength can be kept. However, to increase the strength enough to withstand the centrifugal force due to the high-speed rotation, it is necessary to make thick the thin connection part and to increase the number of the thin connection parts.
Further, at each of the thin connection parts of the rotor 1 of the synchronous motor shown in FIG. 11, the magnetic flux, which is functionally unnecessary, is induced, which causes problems such as reduction of generated torque or low efficiency.
Various methods have been developed and proposed to provide the enough strength to withstand the centrifugal force due to the high-speed rotation with the rotor of the synchronous motor shown in FIG. 11.
For example, the Japanese unexamined patent publication No. JP09-191618 discloses a method to fill the slit with nonmagnetic and electrically nonconductive material to solidify the material. The strength may be increased at some extent by the filler according to this method, however, the bondage between the rotor and the filler cannot be sufficient by simple solidification of the filler. There may be another problem that the increase of the centrifugal force due to the added weight of the filler is larger than the bondage according to the dispersion at the mass production of the rotor and that the strength of the rotor must be increased on the contrary.
FIG. 14 and FIGS. 15A through 15C show methods disclosed by the Japanese Utility Gazette Nos. JP61-199177 and JP61-19917815, respectively, in which a concave and a convex are provided at a side of an aluminum bar of an induction motor. These methods are effective to eliminate a gap between the aluminum and the rotor to prevent the breakage of the aluminum bar due to the vibration. However, the stress concentration to the thin connection part cannot be relieved, since the centrifugal force is received at a thin connection part regardless of the existence of the concave and the convex.